We computed lead free perovskite solar cells based on CsSn _0.5 Ge _0.5 I ₃ can delivered a PCE of 24.20% and unravel the kinetics by Drift-Diffusion simulation. Perovskite/HTM interface was quantify as the “magic” interface that controls the performance.

Perovskite solar cells (PSCs) have experienced a decade of intense investigation as a promising photovoltaic technology, having a power conversion efficiency of 25.5% with the use of lead based light harvesters. Recently, inorganic cesium cation based mixed halide perovskites (CsMI_3−xBr_x, M = Pb or Sn) as absorbers in PSCs gave promising results; in particular CsPbI₂Br demonstrated improved thermal stability and carrier transport properties. However, the performance is far-off from the theoretical limit due to intriguing issues such as high defect density (N_t) and energy level mismatch. Such barriers can be overcome through device modelling and unraveling the kinetics. Here we have employed a computational approach to design and investigate CsPbI₂Br based solar cells by elucidating the role of defect density in the performance and further different types of hole transport layers via optimizing their valence band offset and the barrier height at the back contact was also probed. By optimizing such parameters for CsPbI₂Br, power conversion efficiencies of 17.71, 17.44 and 17.54% using CuSCN, PTAA and spiro-OMeTAD as hole selective layers respectively can be reached. Furthermore, lead free CsSnI_3−xBr_x (0 < x < 3) based PSCs were simulated and the effect of band gap variation as a result of the Br content was studied on the performance. The influence of the defect density of the absorber layer (CsSnIBr₂) at interfaces was studied, and with optimized defect density CsSnIBr₂ based PSCs gave an efficiency of 20.32% with a V_oc of 1.35 V when SnO₂ was used as the electron transport layer and spiro-OMeTAD as the HTM. Our approach suggests ways for experimental design protocols to achieve high performance inorganic Pb and Sn based PSCs.

Deciphering the charge carrier dynamics in perovskite solar cells (PSCs) and electrical merits is essential to further improve the performance and operational stability. We investigated the charge carrier dynamics in triple cation-based PSCs through temperature dependent electrochemical impedance spectroscopy, thermal admittance spectroscopy, and space charge limited current (SCLC). The temperature dependent capacitance versus frequency (C–f) spectra reveal two kinds of activation process, one at low frequency and high temperature (>260 K), and the other at high frequency and low temperature (<260 K). The evaluated activation energy (E_A) at a high temperature from all three experiments was found to be in the range of 0.255–0.266 eV, which corresponds to the activation of the migration of halide anions, while the low-temperature activation process stems from the trapping/de-trapping of electronic charges from shallow traps. The trap density of states in triple cation-based perovskites (10¹⁵ eV⁻¹ cm⁻³) was evaluated to be over two to six orders of magnitude lower than that of typically used single cation-based perovskites, while the charge carrier mobility (5.76 × 10⁻³ cm² V⁻¹ s⁻¹) evaluated from the SCLC technique was nearly an order of magnitude higher than that of single cation perovskites.